Radio Shack TRS-80

MREQ
240
19 2MREQ *"
®
(TO Z23, pins 4 and 12)
SEE
,HEET
2
KEf
IOARD
ROM
@
--
--
ROM
'"
08~
M
07
'T6'
"
AI3 3
J
TO
AI4
4
238
AI5
5
(pi n$
10,12,61
GND
29
MREQ
R9 ®
~~___ D
r ---------~~,
I I
I I
R8 I
QS lOOK •
I MPSS3906 I
I cia + CI4 CRI I
: I~t:~ O'~~eF¢ :~~/:3S :
I I
;;sv I~ 0'11~0~ I
)0 I 29 (32 PLACES) I
; PL AC E::A 37 C2 2,C2 3, C29, I
16-C19 C31,C33,C3S-C38,
I '39 C40,C41, C44-C56 I
L ~
(Revision D and after)
ROM '"
- .,
74LS011l
R62
47K
L--.JVV'v-_-+_---()-+ 5v
Is
14
13
qRJ
Z3
I
4--· I
1.'74 b..;:6 ........ --'M"'E:.:.Mc.....:;'le.-
)-'8~---'S::..j - f I
74LSe0 : ~
I
I
I
I
I __ J I
L ~_--------J
RD'" 13
RAM·
A. Pins 5 and 4 of Z74 connect directly to signal ~MREQ*.
B. Pins 20 of Z33 and Z34 are tied together.
C. DIP shunt Z3, pins 6,7 and 8 are tied together and go to pins 20 of Z33 and Z34.
The signal
is now called ROM*.
D. Pin 39 is now ground. +5 volts still goes to 0.1 MF capacitors (32).
Figure 28. Changes to the TRS-80 Schematic Diagram (Figure 29)
(Revisions D and E)
III